<?php
/**
 * CCacheHttpSession class
 *
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @link http://www.yiiframework.com/
 * @copyright Copyright &copy; 2008-2011 Yii Software LLC
 * @license http://www.yiiframework.com/license/
 */


/**
 * CCacheHttpSession implements a session component using cache as storage medium.
 *
 * The cache being used can be any cache application component implementing {@link ICache} interface.
 * The ID of the cache application component is specified via {@link cacheID}, which defaults to 'cache'.
 *
 * Beware, by definition cache storage are volatile, which means the data stored on them
 * may be swapped out and get lost. Therefore, you must make sure the cache used by this component
 * is NOT volatile. If you want to use {@link CDbCache} as storage medium, use {@link CDbHttpSession}
 * is a better choice.
 *
 * @author Qiang Xue <qiang.xue@gmail.com>
 * @version $Id: CCacheHttpSession.php 2799 2011-01-01 19:31:13Z qiang.xue $
 * @package system.web
 * @since 1.0
 */
class CCacheHttpSession extends CHttpSession
{
    /**
     * Prefix to the keys for storing cached data
     */
    const CACHE_KEY_PREFIX='Yii.CCacheHttpSession.';
    /**
     * @var string the ID of the cache application component. Defaults to 'cache' (the primary cache application component.)
     */
    public $cacheID='cache';

    /**
     * @var ICache the cache component
     */
    private $_cache;

    /**
     * Initializes the application component.
     * This method overrides the parent implementation by checking if cache is available.
     */
    public function init()
    {
        $this->_cache=Yii::app()->getComponent($this->cacheID);
        if(!($this->_cache instanceof ICache))
        throw new CException(Yii::t('yii','CCacheHttpSession.cacheID is invalid. Please make sure "{id}" refers to a valid cache application component.',
        array('{id}'=>$this->cacheID)));
        parent::init();
    }

    /**
     * Returns a value indicating whether to use custom session storage.
     * This method overrides the parent implementation and always returns true.
     * @return boolean whether to use custom storage.
     */
    public function getUseCustomStorage()
    {
        return true;
    }

    /**
     * Session read handler.
     * Do not call this method directly.
     * @param string $id session ID
     * @return string the session data
     */
    public function readSession($id)
    {
        $data=$this->_cache->get($this->calculateKey($id));
        return $data===false?'':$data;
    }

    /**
     * Session write handler.
     * Do not call this method directly.
     * @param string $id session ID
     * @param string $data session data
     * @return boolean whether session write is successful
     */
    public function writeSession($id,$data)
    {
        return $this->_cache->set($this->calculateKey($id),$data,$this->getTimeout());
    }

    /**
     * Session destroy handler.
     * Do not call this method directly.
     * @param string $id session ID
     * @return boolean whether session is destroyed successfully
     */
    public function destroySession($id)
    {
        return $this->_cache->delete($this->calculateKey($id));
    }

    /**
     * Generates a unique key used for storing session data in cache.
     * @param string $id session variable name
     * @return string a safe cache key associated with the session variable name
     */
    protected function calculateKey($id)
    {
        return self::CACHE_KEY_PREFIX.$id;
    }
}
